Insulated wire



Sept. 25, 1928. 1,685,369

E. A. MAU ET AL INSULATED WI-RE Original Filed Ndv. 29. 1922 71 .1 I ig/Patented Sept. 25, 1928.

EDWARD A. MAU AND ORRIN F. HUTCEINSON,

CORPORATION OF MASSACHUSETTS.

01 NEW HAVEN, CONNECTICUT, AS-

SIGNORS, BY MESNE ASSIGNMENTS, TO ROCKBESTOS PRODUCTS CORPORATION, A

INSULATED WIRE.

Application filed November 29, 1922, Serial No. 604,022. Renewed October21, 1987.

This invention relates to insulated conductors and more particularly toconductors which have insulated coverings of such small thickness as tofall within the class of magnet 45 wires.

The invention is directed to the provision of an insulated conductorwhich 1s distinguished by the uniformity and reliability of the coveringwith respect to its electrical insulating properties, the thinness ofthe insulating covering which is a necessary attribute of magnet wireand the adaptability of the insulating covering to rapid manufacture ofthe wire at low cost, using inexpensive i5 short fibres which are notsuitable for general use.

Magnet wire as commonly made heretofore has been of two types, that inwhich the insulating covering is' a composition applied to the wire ina. liquid or plastic state and hardened, and that in which the coveringis made of fibrous material and is .applied'to the wire by wrapping itthereon. The object of this invention is to provide a. magnet wire whichto is superior to these, superior to the film-coatcd wire with respectto reliability and uniformity of the covering as an electrical insulatorand superior to the wrapped wire in that equally well insulated wire maybe manufactured at much less cost. Magnet wire having the film orcomposition coating is deficient in the reliability of its electricalinsulating roperties for the reason that the coating ElCkS the necessaryuniformity and is subject to cracking under flexure, pea-ling,pin-holes, protruding burrs, and soforth, so that the danger of exposureof the conductor or weakening of the insulation at one or more points isalways present. With the wrapped fibre coating, on the other hand, whilethe desired uniformity and reliability of the coating as an insulationmay be secured, the cost of production is relatively high as themanufacturing operation proceeds slowly and relatively 46 expensivelong-fibered staple must be employed in the production of the wrapping.

The insulated conductor constituting the present invention consists of awire having thereon a coating of unspun fibres, preferably cottonfibres, interentangled and densely compacted and having ampleflexibility anda smooth, hard, moisture-proof surface, the coating beingvery thin as is required of the insulating coating of magnet wire, butnever theless of such thickness that at every int the wire is overlaidby a number of Such a coat-ing may be made to adhere to the wire witheat tenacity by the employment of a suitab e adhesive in which theinnermost fibres are embedded, and it is exceedingly tough and amplyflexible. Because of these characteristics, there is no danger of thecoating pealing from the wire or cracking as a result of repeatedflexure of the wire. Also, 1n making such'a coating, it is permissibletouse short-fibre staple which is inexpensive because of its limitedutility for other urposes. Furthermore, it is possible to app y such acoating to a wire by a continuous and comparatively rapid process, muchmore rapid than any wrapping operation, Withthe result that thecompleted conductor may be produced at low manufacturing cost. The fibremay be supplied to the wire in a continuous sliver'which is brought intocontact with the wire after the latter has been coated with an adhesive;then the sliver may be subected to a suitable rub motion whereby it iscaused to enclose the wire and adhere to it; and then as the Wire is fedalong, it is subjected to rapidly rotating pressure devices which serveto compact the fibrous coating to a great density and give it a hard,glazed and preferably water-proofed' surface while retalnlng itstoughness and flexibility.

It has been proposed heretofore to insulate electrical conductors withan insulating coating of interentangled fibres, such for instance ascotton or asbestos, but this has been done only in connection-with themanufacture of so-called fixture wire in which the thickness of theinsulatin coating is a matter of little importance, mechanical strengthto withstand blows and strains the fixture being the importantconsideration. So far as we are aware, a magnet wire with a thin, dense,tough, flexible and uniform coating of unspun interentangled fibres hasnever been produced heretofore successfully.

In a conductor having an insulating coating of this nature, it is of theutmost importance to insure that the conductor shall be overlayed by asubstantial number of fibres at every point, and this requisite must notbe sacrificed to any appreciable extent in order to secure thinness ofthe coating, for thorough electrical insulation is a primary requisite.The attainment of this desirable characterincident to the handling of.

istic is made more certain by so applying the fibres to the wire thatthey will be arranged more or less-in accordance with a prescribedorder. Very desirable results with respect to uniformity of the coatingmay be obtained by so applying the fibrous covering to the wire that thefibres close tov thewire are arran ed generally parallel to the lengthof the wlre, whereas the fibres further from the wire are arrangedinsome other manner, as for instance, in a generally circumferentialrelation. This form of covering presents two important advantages,first, it results in the attainment of a greater degree of uniformity inthe dielectric strength of the insulation, and second, it permits of theuse of simple and inexpensive manufacturing expedients.

Another consideration of importance is that the electricalcharacteristics of the wire must not be deteriorated by the applicationof the covering to the wire. If the process employed be such that thewire is worked to any considerable extent it will become fatigued andits conductivity will be lowered. For instance, if the application ofthe fibrous covering to the wire be effected by the employement of a rubmotion apparatus, this should not be so operated as to result in rollingof the wire back and forth upon itself ashas been the case withapparatus of this character heretofore proposed. The best results areattained when the process and apparatus for applying the insulatingcovering are such that the wire passes through the apparatus with theminimum of bending and no movement about its axis, with the result thatits electrical conductivity is not impaired at all.

The invention will be better understood by reference to the followingdescription taken in connection with the accompanying drawings whichillustrate the conductor and also the apparatus which may be employed inmaking it.

Referring to these drawings, Fig. 1 is a view on an enlarged scale of ashort length of magnet wire embodying the invention; Fig. 1 is a similarview many times enlarged;

, Fig. 2 is a transverse section of the wire shown in Fig. 1; Fig. 3 isa view in elevation of ap paratus for producing the wire; Figs. 4 and 5are similar views of apparatus employed in later stages of the process;Figs. 6 and 6 are sections on lines 6-6 and 6**6 of Fig. 4; and Figs. 7and 8 are detail views of wiping and polishing devices being sections onlines 7-7 and 8-8 respectively of Fig. 5.

Figs. 1, 1 and 2 show the insulated wire embodying the invention, thewire'being indicated at 10 andthe insulating covering at 11. The wireitself may be of any size and of any material. The insulated covering 11on the wire is a highly compacted, uniform, tough and flexible coatingof unspun interentangled fibres snugly adhering to the wire and having asmooth, water-proofed surface.

wire by being imbedded in a suitable adhesive 7 whereas the fibres. inthe outer portion of the covering are arranged generallycircumferentially.

In Fig. 1*, the reference 11' indicates the innerportion of theinsulatingcovering in which the fibres are arranged generally parallelto the length of the wire. The fibres of the outer portion of thecovering are considerably interentangled but their arrangement isgenerally circumferential. This arrangement of the fibres of 'thecovering conduces to uniformity of dielectric strength, flexibility andinsurance against weakening of the insulation by fiexure of the wire.

A wire having these properties may be made by the employment of themethod and apparatus indicated in Figs. 3 to 8 inclusive of thedrawings. In Fig. 3, 12 indicates the doifer roll of a finishingcardprovided with a comb 13 which acts to strip slivers of carded cottonor like fibres from the usual rings of the dofi'er roll. The sliveris'shown'at 1 and after it leaves the roll 12 it is sustained by a belt orconveyor 14 having transversely disposed ribs 16 thereon. The stockemployed in making the sliver may be any grade of cotton or other fibre,well ginned and cleaned; the grade of cotton fibre commonly known ascombings may be employed to advantage. One of the valuablecharacteristics of the wire of this invention is that high insulatingproperties may be attained in an insulating covering made of short fibrestaple which is very inexpensive because its field of utility is solimited.

The conductor to which the insulation is to be applied is shown at 15.It is guided by suitable rolls through a bath of adhesive 2 and thenpasses up beside the roll 12 to the upper surface of the belt 14 whereit comes in contact with the under side of the sliver 1 and travelsalong upon the surface of the belt 14 with the sliver. Of course, aplurality of wires may be treated at the same time, these being arrangedin parallelism for coaction with slivers 1 which are dofi'ed from theroller 12 in parallelism.

diameter of the wire to be covered and the wire is so guided andsustained that it is centrally located with respect to the sliver. Asshown in Fig. 6, the sllver overhangs the wire at the sides as thesliver and wire leave the belt 14. From the belt 14 the sliver andwirepass to ether at the same speed between rub motion elts 17 and 18located in close proximity to the transfer belt 14. These rub motionbelts have a longitudinally progressing and laterally reciprocatingmotion. This reciprocating motion produces a rolling or twisting of thesliver about the core but care is exercised in so positioning the beltsthat in rollin the sliver upon the wire they will not roll the wire uponitself. Such rolling ofthe wire is exceedingly detrimental to the wire'for it has the effect of hardening it and therebydecreasing itselectrical conductivity. The action of these rub motion belts applies.the sliver to the wire entirely around the wire and causes a substantialportion of the fibres of the sliver to be imbedded in the adhesive andthese-ends are accomplished without disturbing the uniformity of thedistribution of the fibres lengthwise of the sliver. As a result, theproduct leaves the rub motion belts in the manner indicated in Fig. 6with the wire enclosed centrally Within a substantially circular body offibres which are more or less condensed and in which the fibres at theinterior of the body are imbedded in the adhesive on the wire.

While we have shown and described above,

certain operations and apparatus by the use of which a sliver or body offibres is caused to be first applied to a conductor-or core member anddistributed substantially uniformly thereabout without disturbing thegeneral lengthwise or substantially parallel arrange ment of the fibresadjacent the wire or core, after Which subsequent steps are performed,as described, we do not limit ourselves to these specific preliminaryoperations as described or to the form of apparatus as specificallyshown. Other operations and other forms of apparatus may be employed,provided suitable means are supplied whereby the fibres will first besubstantially uniformly distributed about and generally parallel to thewire or core member adjacent the surface thereof, and provided thefibres adjacent the surface of the wire or core member are maintainedgenerally parallel thereto or lengthwise thereof during the subsequentoperations during which the remaining or outer fibres of the coveringare indiscriminately entangled or are inter-entangled and arrangedgenerally circumferent-ially of the wire.

From the rub motion belts the product passes to a wiping device orlicker 19 which may consist of a pair of flat springs adapted to engageopposite sides of the wire and to be rotated by suitable means, notshown, as the The wire is then carried through a mois- I ture-proofingmedium 22 which may be in a receptacle 20 having a pulley 2lvmountedtherein around which the wire passes. A compound of nitrocellulose iswell adapted for use as the moisture-proofing medium as a coating ofthat substance not only protects the insulating covering from moisturebut also serves to cement down the fibres of the insulating body andhold them permanently in close contact.

From the receptacle 20 the wire passes to a wiper 23 which is of thesame general nature as the licker 19. This wiper serves to remove excesssolution from the fibre body and further condense the later preparatoryto the polishing operation.

The polishing may be performed by a suitable die 24 which may be locatedin close proximity to'the wiper 23. This polishing device may consist ofa pair of polishing blocks 25 shown in detail in Fig. 8. These blockshave opposing smooth polishing surfaces between which the wire passes.The function of the polishing device is to condense the fibres of thecovering to a high degree and further entangle and mat them to bring thecovered wire to the required gauge and compact the fibrous insulatingcovering to the desired density.

By the employment of such a process and apparatus, a wire may beprovided with an insulating covering which is of the thinness of magnetwire insulation and which is of pronounced uniformity of thickness anddielectric strength and of such toughness and elasticity that it willnot be broken or Weakcned by repeated flexure of the Wire. The operationof applying this coating to the wire is an inexpensive one because theinsulating of the wire proceeds with far greater rapidity than anybraiding or wrapping operation and the cost of the completed wire isfurther reduced by the fact that this form of insulation permits of theuse of short fibre staple which is inexpensive. Also, the nature of theoperation is such that the electrical properties of the Wire are notaltered by the operation of applying the coating to the wire as theywould be if the wire were rolled back and forth upon itself as anincident to applying the fibrous covering to it uniformly for suchrolling motion of the wire would covered are approximately 7 fibres one'on top of an other at every point over the surface of the wire, thesefibres being cries-crossed and interentangled more or lessindiscriminately.

When the conductor is flexed the fibres running more or less in thedirection of the length of the wire are particularly effective inmaintainin the integrity of the covering. Thus, fibres w ch lie adjacentto the wire are arranged generally parallel tothe length of the wire; tthe fibres in the sliver 1 areinitially arranged in substantialparallelism and the fibres close to the wire become imbedded in theadhesive more or less before the wire and sliver arrive between the rubmotion belts. The action of these belts causes a greater imbedding ofthe fibres in the adhesvie and carries the sliver entirely around thewire. In the later operations, particularly that of the polishin device24, the body of fibres is compacte and as an incident to that the fibreswhich are not securely imbedded in the adhesive are given a generallycircumferential direction about the wire.

While we have shown and described a preferred embodiment of ourinvention, it is 'to be understood that the same is not to be limitedthereto in all of its details, as modifications and variations may bepossible, which will lie within the spirit of the invention and thescope of the appended claims.

We do not claim herein the method of insulating wire as described andclaimed in our copending application, Serial No. 238,178, filed December6, 1927, nor the apparatus for insulating wire as described and claimedin our copending application, Serial No. 238,179, filed December 6,1927.

We claim:

1'. An insulated electrical conductor comprising a wire and aninsulating sheath for the wire consisting of a tough, flexible cover ingof densely compacted fibres, the fibres of the covering adjacent to thewire being generally parallel to the length of the wire and is is dueprimarily to the fact that entangled fibres, the fibres the remainingfibres being indiscriminately entan led.

insulated electrical conductor com- .prismg a mm and an insulatifisheath for the wire consisting of a tough, exible covering of denselycompacted bres, the fibres of t e coverin adjacent to the wire beinggenerally para el to the length of the wire and the remaining fibresbelng interentanled and arranged generally circumferentialy of the wire.

insulated electrical conductor comprising a wire in a substantiallyunfatigued condition and an insulating covering for the wire comprisinga highly compacted,uniform,

.tough, flexible and moisture-proofed coating of fibres, the fibres atthe interior of the covermg being generall parallel to the length ofthe. wire and imbe dad in an adhesive on the wire and the remainingfibres being inter- I entanlgled but arranged generally circumferentia yof the wire.

4. An insulated electrical conductor, comprising a core member and aninsulating sheath for said core member, comprising a densely compactedmass of fibres, the fibres directly adjacent the core member beindirected generally parallel to the length thereof, the remaining fibresbeing indiscriminately intermingled, and all the fibres of the coveringbeing interentangled with each other, and means to bind all of thefibres together.

5. In an electrical conductor, the combination of a core member and acovering therefor, comprising a densely com acted mass of entangledfibres, the fibres being directed generally parallel to the length ofsaid core member adjacent the same, and turned to a position whereinthey are generally directedcircu'mferentially of the core member at theouter surface of the covering, and means to bind said covering to saidcore member.

6. In an electrical conductor, the combination of a core member and acoveringtherefor, comprising a densely com acted mass of bein directlygenerally parallel to the length 0 said core member adjacent the same,and gradually turned to a position wherein they are gen erally directedcircumferentially of the core member at the outer surface of thecovering, means to bind said coverin to said core member, and means tobind a l of the fibres together.

In testimony whereof we afiix our signatures.

- EDWARD A. MAU.

ORRIN F. *HUTGHINSON.

